As shown in FIG. 3, a working vehicle 101 such as a mobile crane is provided with an engine 111, and power of the engine 111 is transmitted to a wheel 102 through a torque converter 112, a transmission 113 and the like so that a running operation is enabled by a running vehicle body. Moreover, the power of the engine 111 is also used to drive a hydraulic pump for a hydraulic working device 115. A hydraulic oil 122 in a hydraulic oil tank 114 is supplied to the hydraulic working device 115 such as a crane device to enable a work through the hydraulic working device 115.
The working vehicle 101 includes a radiator 116. Engine cooling water 121 is circulated between the engine 111 and the radiator 116 so that the engine 111 is cooled. Moreover, the working vehicle 101 includes an oil cooler 117 and the hydraulic oil 122 is thus cooled. A torque converter oil 123 to be used for the torque converter 112 and the transmission 113 is heat exchanged with the engine cooling water 121 by a heat exchanger 118 and is thus cooled.
In a work carried out by the hydraulic working device 115, heat of the engine 111 is radiated by the radiator 116 through the engine cooling water 121 and the heat of the hydraulic oil 122 is radiated by the oil cooler 117. On the other hand, in a running operation carried out by the running vehicle body, the heat of the engine 111 is radiated by the radiator 116 through the engine cooling water 121 and the heat of the torque converter oil 123 is exchanged with the engine cooling water 121 so that the heat is radiated by the radiator 116. The hydraulic working device 115 is not operated and a temperature of the hydraulic oil 122 is not raised. For this reason, the oil cooler 117 does not work substantially.
Regardless of heat generation from both of the engine 111 and the torque converter oil 123 in the running operation, thus, the heat is radiated from only the radiator 116 and the oil cooler 117 does not work. For this reason, there is a problem in that cooling cannot be performed efficiently. In high load running for an upward slope or the like, particularly, both of the engine 111 and the torque converter oil 123 generate heat in large amounts. In order to obtain a sufficient cooling effect, therefore, the radiator 116 is required to have a large size.
Patent Document 1 discloses the technique for cooling a torque converter oil by exchanging heat between the torque converter oil and the hydraulic oil in a fork lift truck. However, an oil cooler for cooling the hydraulic oil is not provided.